Method of oxidizing aiotonia



W'. S. LANDIS.

METHOD 0F OXIDIZING AMMONIA. y APPLICATION FILED FEB. zo, Isls. IIENEwEDIuNE I5, I9Ie.

1,1 93,796. j Patented Aug. 8, 1916.`

Mllll Billllllllllllllllllllllglll'l- 'WALTER S. LANDIS, OF NIAGARAFALLS, NEW YORK, ASSIGNOR TO FRANK S.

i WASHBUBN, OFNASHVILLE, TENNESSEE,

METHOD OF OXIDIZING AMMONIA.

Specieation of Letters Patent.

Application led February 20, 1915, Serial No. 9,595. Renewed June 15,19.16. Serial No. 103,864.

To all whom z't may concern.'

Be it known that I, WALTER S. LANDIS, va citizen ofthe United States,residing at Niagara Falls, in the county of Niagara and Statev of NewYork, have invented certain A new and useful Improvements 1n Methodsprovide a method which will be more elicient in action and less costlyto operate on a commercial scale than those heretofore roposed.

With this and other objects in view, the invention consists in the novelsteps constituting my process and in the novel combinations of partsfound in my apparatus, all as will be more fully hereinafter disclosedand particularly pointed out in the claims.

Referring to the accompanying drawing forming a part of thisspecification, wherein the figure is a diagrammatic longitudinalsectional view of one form of apparatus suitable for carrying out myprocess: 1 represents a main for conveying a suitable mixture ofammonia, NH3 and air, 2 a connecvtion between sald maln 1 and the1ns1deof the shell 3 of the apparatus, and 4, a valve in the connection2. The inside of the shell 3, or the oxidation chamber 15, may be ofAany suitable size or shape, and is made of any suitable material whichwill be inert to the contained gases, at temperatures of say 700 C. andhigher.

In the chamber 15, is located the cooler 16, which is convenientlyformed somewhat like the usual type of automobile radiators. That is tosay said cooler is conveniently made of very thin sheet material,providing small cells or passages 17, through which the gases may pass,and is also provided with-passages not shown for a cooling fluid such aswater, or other cooling agent extending at right angles to said passages17. As it is desirable to keep the temperature as low as posible. onemay use any suitable refrgerating fluid in the cooler 16. Said coolingfluid is conveniently led to the passages of the cooler 16, as by thepipe 5, con- Patented Aug. 8, 1916.,

nected to the cooler by the pipe 6, provided i with the valve 18, all aswillv be clear to those entday automobile radiators.

7 represents a suitable -siphon connected to the cooling fluid passagesof the cooler 16, for the purpose of draining the same, and said siphonconveniently discharges into the drain 8. Immediately above the cooler16, is located the catalytic material 9 preferably composed of finelydivided platinum material and through said material 9, I preferably passa resistor 19, having the lead wires 10, for the purpose of raising thetemperature of said material 9 to the desired point to insure thestarting of the `catalytic reaction, and for the purpose of alsomaintaining said material at that temperature found necessary to insurethe continuance of said reaction.

The nitrose gases will pass through the catalyzer 9 and collect in thechamber 20, whence they may be drawn oil through a connection 21,provided with a valve 22, leading to the main 23. Of course, it will beunderstood that a plurality of apparatus -such as that disclosed `may besuitably joined with the mains l, 5 and 23, and the process carried onsimultaneously in each.

In order that the difference between my process and those which havegone before may be the more clearly understood it is said: The oxidationof ammonia to nitric oXid has been the subject of experiment andinvention for probably seventy years, but up to the present time it hasmade practically no commercial headway. One reason for this `failure toattain a place for this process in the industrial world can be ascrlbedto the following: (a) The degree combustible in air, like illuminatinggasor hydrogen, because its caloriic intensity when burned in thismanner, is so much below its ignition point that the combustion cannotpropagate itself. I have calculated that whereas temperatures of upwardof 700 C. are necessary for the propagation or the. combustion ofammonia', yet one obtainvy 2 '95 of attainable combustion has been verylow R which entailed serious losses of the valuable only about 450 C. byits direct combustion in air,'under ysuch proportions of mixture aswould insure the ammonia burning to nitrose gases. In oxygen of courseit burns without diiiiculty, according to the reaction:

If. one desires to write a similar equation representing the combustionin air, we'can Y assume that the air consists approximately of @Nfl-02)so that our equation would readani-13,625 @M+-go.) =aNo+ sH2o+2oN2 Thisyields the valuable nitric oxid which can be converted by well knownmethods into nitrous or nitric acids, or corresponding salts of thesame. But as a matter of fact this catalytic combustion with air, orwith oxygen, requires more than the theoretical quantity of oxygen toinsure com-Av plete combustion, and I find it necessary to use from l to2.2 times the theoretical quantity of air, the excess passing through'unchanged. Naturally using such an excess of air as above indicated,the flame temperature will be very much lower than that necessary formaintaining combustion. In order, therefore, to assure a continuouscombustion of the ammonia it is necessary that some means of supplyingheat to the reaction be employed, otherwise the flame will go out, evenif started. Many inventors 1n this field have supplied this additionalheat in their commercial forms of apparatus by preheating' the mixtureof air and ammonla through a regenerative arrangement of apparatus,whereby a portion of the heat 1n the products of combustion istransferred to lthe reagents. This portion of heat must be suflicient tomake up that deficiency whlchthe reaction does not supply, so as toinsure a flame temperature of some 600o C. to 700 C. necessary7 for acontinuous propagation ofthe same. It is likewise well known thatammonia gas is decomposed into nitrogen and hydrogen by heating tocomparatively low temperatures; and, therefore, any considerablepreheating of the ammonia-air mixture will cause a decomposition of theammonia before it strikes the catalyzerfand so cause 'a low efficiencyof transformation to nitrose gases. It is true thatunder certainconditions this preheating may not be suiiicient to raise thetemperature of the alnmonia to a point Where a serious decompositionwill result, but when one considers that the temperatures. of thecatalyzers in use are quite close to the flame telnperature, and,therefore, can radiate a large quantity of heat back into the oncominggas current, we can readily see that the intentional preheating plus theabsorbed radiated heat creates temperatures in the ammonia-air mixturewhich can cause a considerable decomposition of the ammonia. It isfurther readily seen that under certain conditions this dissociation maytake place to only a small extent, thereby setting free operating uponthis principle decompose from 5 to 15% of the ammonia by a combinationof the above causes beforel the ammonia-air mixture ever strikes thecatalyzer, and, therefore, they yield a correspondingly low efficiencyof transformation of ammonia into nitrose gases.

I have discovered the above 'objections and obtain very much Vhigherefliciencies inthis transformation o f ammonia into nitrose gases by thefollowing general combustion principle: Instead of preheating themixture before-it is brought up to the catalyzer I intentionally coolit.

The more energetic this' cooling is the higher the efficiencies, andwith some recent types of my apparatus, described .in my copendingapphcation Serial No. 9596 filed Feb. 20, 1915, and entitled Process ofand apparatus for oxidizing ammonia, I have succeeded in gettingessentially 95% andl above, of the ammoniaitransformed into nitrosegases.' The best results would naturally be obtained by having a veryenergetic cooler lplaced approximately one molecular diameter of ammoniafrom the catalyzer surface, but it is self-evident that structuraldifficulties render impossible the placingA of these two things so closetogether, and I, therefore, must limit myself to placing the cooler asclose to the hot catalyzer as constructive details will allow. It isalso self- Aevident that various forms of apparatus for carrying outthis process can be used and the one disclosed above is therefore onlyan example of one form. Accordingly in carrying out my process, Ipreferably mix thel ammonia gas NH3, with s ay an excess of from 1li to2,12- times the theoretical quantity that I can overcome of air, deliverit to the main 1 which distributes the mixture under pressure throughconnections 2 to a plurality of lcombustion chambers 15, and the valves4, are so regulated as to cause said mixture to pass through the cells17 of the coolers 1.6 and through the catalytic masses 9, at such a rateas will produce the best results.

In order to avoid the wasteful dissociation of the ammonia that has beenheretofore encountered due to thepreheating of the mixture, Il cool saidair-ammonia mixture as much as is convenient as it passes through thecooler 16 thereby keeping said mixture below say 400O C. or below itsdissociation point before it reaches'the catalyzer. 'In other words inorder to prevent theammonia from receiving too much heat from the hotcatalyzer just before it reaches the latter, and thereby causing adecomposition to take place, I subject the mixture to the action of thecooler 16, .which not only cools the ammonia, but it also prevents the-radiant heat of thehot catalyzer from reaching the on coming ammonia.In order that the action of the cooler 16 may be better understood itmay be said: Ammonia mixed with air begins to decompose at temperaturesupward of 25W-300 C. and this decomposition is extremely rapid attemperatures approaching redness. If now a mixture of air and ammonia isbrought-I up to a catalyzer of such formas to insure an oxidation of theammonia that strikes it, and the ammonia is not heated above 300 beforeactually coming into contact with the catalyzer no substantialdecomposition will result. The catalyzer is, howevenusually at atemperature of about 60Go-700 C. and, therefore radiates heat rapidlyinto the on-corning ammonia. monia-air mixture usually prior to myinvention becomes heated to over 300 C. at a small distance from thecatalyzer itself. Decomposition has usually, therefore, immediatelytaken place prior to my invention withv a consequent loss in eiciency oftrans- 'Ihis invention provides-a remedy for this trouble by theinsertion of a cooler immediately in front of the catalyzer which actsto prevent radia-jtion of the heat from the catalyzer back into theori-coming stream of. ammonia gas so that the ammonia may even reach thecatalyzer at or below ordinary roomlemperatures. As the distance betweenthe cooler and the eatalyzer is made extremely small in this apparatus,there is practically no opportunity given for 'the radiant heat from thecatalyzer to increase the temperature 0fI the ammonia-air mixture,before said mixture strikes the catalyzer, and consequently,

-I obtain a very much higher leflic'iency of transformation of ammoniathan has been obtained heretofore. Further, in order to insure that thetemperature in the catalyzer shall be maintained sufliciently high toinsure an efficient oxidation of the ammonia and thereby prevent theexcess of air and other conditions from unduly reducing the As a result,this on coming am-A 19 and circuit 10. It will thus be seen thatIpreferably provide an excess of air in the mixture, I cool the mixtureinstead of heating it', and I maintain a temperature above 5000 C. andup to say 700 C. or higher in the catalyzer to which the mixture isdelivered. I further place the catalyzer as close to thecooler aspossible, so as to beable to deliver the mixture at as low a temperatureas possible to said catalyzer.

vIt is ofcourseA self-evident that to turn the apparatus upside down andpass the ammonia-air mixture downward instead of upward, or to turn itsidewise and pass the current horizontally would in no Wise adect thegeneral principles of the invention. SimilarlyI do not wish to limitmyself to the distance I place the cooler and the catalyzer apart,because that is a matter of structural design only and varies with thedifferent mixtures used, or the degree of combustion one desires toeffect. I 'have found it possible to work .as close as 0.04 inch withouttrouble. I have also discovered that I can replace the air in my mixturewith oxygen, in which case the combustion will take care of itself afterit is oncestarted. In the case of the use of oxygen the temperaturestend to rise -so high ,in the -catalyzer that some dissociation of thenitrose gases occurs, and then I find it convenient to place my coolerso close to the catalyzer that I absorb a large amount of the heat ofthe reaction from this apparatus by direct radiation into my cooler. Bythis expedient I can keep the temperature down to such a point that nodissociation takes place. I can also use various mixtures of oxygen and'105 air, or enriched air in my apparatus, controlling-excessivetemperatures by the degree of cooling attained by my cooler. I havefurlther found it convenient to cover the cooler 16 with a Wire gauzefabric such as 25, in 110 order to. more effectually' cool the catalyzer9.

. It is therefore obvious that those skilled4 'in the art mayvary thedetails of my appa- -ratus as well as of myl process without departingfrom the spirit of my invention and therefore I do not Wish to belimited to the above disclosure except as may be required by .theclaims.

What I claim ise 12o 1. The process of oxidizing. ammonia which consistsin mixing air with said am- 2. The process of oxidizing ammonia heatedcatalyzer; and subjecting said mix ture to a cooling meansv adapted tocut off j. radiant heatjust before `it reaches said cata-1yzer,substantia11yyas described. A

which *consists in passing a' mixture 4containing ammonia and oxygenthrough a 3. The process of oxidizing ammonia Which consists inproviding a mixture containing ammonia and oxygen in suitableproportions; subjecting. said mixture to a `cooling means adapted to cutoif radiant heat just before it reaches thecatalyzer;

subjecting the cooled mixture to the'action of the heated catalyzer; andmaintaining the 'temperature ofsaid oataljizr above l500" 15.C.,ysubstantia11y as described.

4. The -process of oxidizing ammonia which consists in mixing saidammonia with i

